Superconducting article with compliant layers

ABSTRACT

A composition for a plurality of configurations of a high-temperature superconductor tape including a superconducting film disposed on a compliant film or sandwiched or captured between at least one pair of compliant film layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. § 119(e) of U.S.Provisional Patent Application No. 61/668,137 filed on Jul. 5, 2012,titled “Superconducting Article with Compliant Layers” the entiredisclosure of which is hereby incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

BACKGROUND

Field of the Disclosure

This disclosure relates to superconductors and more specifically to themechanical and electrical properties of superconducting tapes.

Background of the Disclosure

Several materials and systems have been researched in order to solve thefuture problems with energy generation, transmission, conversion,storage, and use. Among many potential solutions, superconductors mayrepresent a unique system solution across a broad spectrum of energyproblems. More specifically, superconducting structures, includinghigh-temperature superconducting (HTS) tapes, enable high efficienciesin generators, power transmission cables, motors, transformers andenergy storage. Further, superconductors may have applications beyondenergy to medicine, particle physics, communications, andtransportation.

Conventionally, there are about nine components in a typicalsecond-generation high-temperature superconducting (2G HTS) tape. Thearchitecture consists of several oxide films on a metallic substrate andcapped with silver and copper over-layers. The composite structure isprone to issues such as debonding between individual layers anddelamination within the superconductor layer. Transverse tensilestrength measurements on some conventional 2G HTS tapes, wherein atensile stress is applied normal to the tape's surface, have shownevidence of weakness. A uniform pull or stress may be imparted on thetape by means of Lorentz force acting mutually perpendicular to atransport current flowing through a superconducting tape in conjunctionwith an externally applied magnetic field. The fracture surfaces of the2G HTS tape provide insight into the interfaces and films architectureor structures that are prone to debonding and delamination. Morespecifically, the interface between the LaMnO₃ (LMO) top buffer layerand the REBa₂Cu₃O_(x) (REBCO) superconducting film has been found to beprone to debonding and the REBCO itself has been observed to be prone todelamination within the overall architecture of the HTS tape.

Additionally, evidence of weak transverse strength in tapes in coilsfabricated with epoxy impregnation has been observed. The difference inthermal expansion coefficients of the tape and epoxy may result in thetransverse stress on the tape. Thus, if the tolerance of the tape tothis stress is low, then coil degradation may occur. Further, as asignificant proportion of the applications of 2G HTS tape involve coilgeometries, this mechanical weakness poses a significant problem in thedeployment of 2G HTS tapes to these industries. Another source ofweakness within the REBCO film structures is the presence of secondaryphases, such as copper-oxide (CuO) and misoriented a-axis grains. Theseinhomogeneities in the microstructure provide crack propagation pathsthat may result in reduced transverse tensile strength, as well asdecreased current carrying capacity, or critical current, of thesuperconductor, and may be detrimental to other electrical properties.Thus, there is a demand for a HTS tape having improved transversetensile strength and electrical properties for commercial applications.

BRIEF SUMMARY

Disclosed herein is a high temperature superconducting tape architecturewith a plurality of configurations to improve the mechanical andelectrical properties therein. More specifically, in one exemplaryconfiguration, the HTS tape includes the superconducting film sandwichedor captured between a compliant film and the overlayer. Additionally,another exemplary configuration comprises a superconducting filmdeposited on a composite of oxide and a compliant material.Additionally, an extrapolation of this configuration may includealternating layers of superconductor films with compliant material.Further, the superconducting film deposited on LMO, or other oxidebuffer surface, with an array of nanoparticles of a compliant materialis disclosed herein. In other exemplary configurations, thesuperconducting film may include randomly distributed, compliantparticles, or include an embedded layer of compliant nanomaterials, andin certain instance, the tape may comprise multiple layers thereof.

Further, there is disclosed one configuration of a superconductor tapestructure comprising a substrate, compliant material layer, asuperconducting layer overlying the compliant material layer, and anoverlayer. The compliant material layer may comprise an epitaxially orbiaxially oriented layer and at least one material chosen from the groupconsisting of metals, alloys, ceramics, and combinations thereof.Further, the compliant material may comprise a high ductility or a highfracture toughness, such as but not limited to a composite of an oxideand a metal or alloy, such as but not limited to silver.

Also, there is disclosed a superconducting tape comprising a substrate,a first superconducting layer, a compliant material array, a secondsuperconducting layer, and an overlayer. In exemplary configurations,the compliant material array comprises nanoparticles having a size ofless than about 0.5 μm disposed between the first superconducting layerand the second superconducting layer. In some configurations, thesuperconducting tape structure comprises a substrate, a plurality ofsuperconducting layers, a plurality of compliant material layers,wherein at least one of the plurality of the compliant material layerscovers at least 15% of the surface area of the layer beneath it.Further, in some configurations, at least one of the compliant materiallayers comprises at least one epitaxially oriented layer.

In another configuration, a superconductor structure comprises asubstrate, a compliant material array comprising nanoparticles having asize of less than about 0.5 μm, a superconducting layer, and anoverlayer. In some instances, the compliant material array comprises atleast one material chosen from the group consisting of metals, alloys,ceramics, and combinations thereof, having a high ductility or highfracture toughness, and covering at least 15% of the surface area of thelayer beneath it. In certain instances, the compliant material comprisessilver.

Also disclosed a superconductor structure comprising a substrate, afirst superconducting layer, a compliant material layer, a secondsuperconducting layer, and an overlayer. In certain configurations, eachof the first and the second superconducting layer has a thickness ofless than about 1 μm. Further, the compliant material layer may bedisposed between the two superconducting layers. In some configurations,the compliant material layer comprises a biaxial textured materialchosen from the group consisting of metals, alloys, ceramics, andcombinations thereof.

The embodiments described herein comprise a combination ofcharacteristics and features intended to address various shortcomingsassociated with certain prior compositions, combinations and devices.The various characteristics and features described above, as well asothers, will be readily apparent to those skilled in the art uponreading the following detailed description and by referring to theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

For a detailed description of the exemplary configurations of thedisclosure, reference will now be made to the accompanying drawings inwhich:

FIG. 1 illustrates a schematic cross-sectional microstructure of aconventional thin film superconducting tape adjacent to aphotomicrograph thereof;

FIG. 2 illustrates the two examples of the fracture surfaces of aconventional superconducting tape after debonding and delaminationduring testing at high transport current and high magnetic field, thelight regions are the top buffer layer and dark regions are the exposedsuperconducting layer;

FIG. 3 illustrates the (a) top-surface and (b) cross-section of anexemplary super-conducting film on Ion Beam Assisted Deposition (IBAD)MgO template on flexible metal substrate, with a thickness of about 2μm;

FIG. 4 illustrates the (a) XRD theta/2-theta (θ/2θ) pattern of Ag bufferepitaxially grown on MgO-buffered metal substrate and (b) XRDpole-figure of the epitaxial Ag buffer;

FIG. 5 illustrates (a) a schematic of a compliant material having adiscontinuous array of nanoparticles on oxide buffer on which thesuperconductor film is deposited and (b) the microstructure of ananoparticle array of silver created on an oxide buffer on IBAD templateon metal substrate.

FIG. 6 illustrates a schematic of an exemplary 2G HTS tape architecturehaving nanoparticle arrays in between layers of superconducting film;

FIG. 7 illustrates a schematic of a 2G HTS tape architecture withcompliant material nanoparticle arrays on the oxide buffer surface andwithin the superconducting film;

FIG. 8 illustrates schematic of an exemplary 2G HTS tape architecturehaving alternating superconductor and compliant material films.

DETAILED DESCRIPTION

As shown in FIG. 1, there are typically about nine components in aconventional 2G HTS tape. The architecture consists of several oxidefilms on a metallic substrate and capped with silver and copperoverlayers. Generally, the composite structure is prone to de-bondingbetween individual layers and delamination within the superconductorlayer. 2G HTS demonstrate these potential weaknesses wherein a tensilestress is applied normal to the tape's surface for example, when auniform pull is imparted on the tape by means of Lorentz force actingmutually perpendicular to both a transport current flowing through asuperconducting tape and an externally applied magnetic field. Duringthese tests, the fracture surfaces of the 2G HTS tape reveal theinterfaces and films that may exhibit high frequencies of debonding anddelamination.

Referring now to FIG. 2, the photomicrograph illustrates examples of thefracture surfaces resultant from debonding and delamination of aconventional tape. FIG. 2 specifically illustrates that the interfacebetween the LaMnO₃ (LMO) top buffer layer and the REBa₂Cu₃O_(x) (REBCO)superconducting film is prone to debonding under these transversestresses. Meanwhile, the REBCO itself is prone to delamination withinthe layer as shown in the FIG. 2. Additionally, it is known that coilsfabricated with epoxy impregnation are poorly resistant to transversestresses. Specifically, the thermal expansion coefficient differencesbetween the tape and the epoxy may result in sufficient transversestress on the tape causing it to debond or delaminate. Further, if thetolerance of the tape to this degradation is low, then coil degradationoccurs. Generally, the expected 2G HTS tape applications involve coilgeometries, and this mechanical weakness poses a significant barrier tothe implementation and deployment of 2G HTS tapes commercially.

Disclosed herein is a novel HTS architecture intended to improve thetransverse tensile strength of 2G HTS tape. As discussed herein, onesource of weakness within the REBCO film is the presence of secondaryphases such as CuO and misoriented a-axis grains. For example, referringto FIG. 3, the microstructure of the top surface and cross section of a2 μm thick REBCO film in a 2G HTS tape shows an abundance of a-axisgrains (a) and CuO (b). These inhomogeneities in the microstructurecould provide paths of crack propagation resulting in reduced transversetensile strength and reduction in the electrical properties of an HTStape, in particular, the current carrying capacity, or critical current,of the superconductor.

Thus, the disclosure herein includes a plurality of configurations of ahigh-temperature superconductor (HTS) tape designed to improve themechanical and electrical properties therein. More specifically, in oneexemplary configuration the HTS tape includes the superconducting filmsandwiched or captured between a compliant film and the overlayer, forexample a silver overlayer. In instances, the overlayer serves toprotect the superconducting film from the environment. Additionally,another exemplary configuration comprises a superconducting filmdeposited on a composite of oxide and a compliant material. Further, anextrapolation of this configuration may include alternating films ofsuperconductor films with compliant material. Further, thesuperconducting film deposited on LMO, or other oxide buffer surface,with an array of nanoparticles of a compliant material is disclosedherein. In other exemplary configurations disclosed herein, thesuperconducting film may include randomly-distributed, compliantparticles, or include an embedded layer of compliant material comprisingnanoparticles, and in certain instances, the tape may comprise multiplelayers thereof.

In certain instances, the present disclosure is related to forming anHTS tape having a compliant material component therein. As used herein,a compliant material is any that is ductile, exhibits high fracturetoughness, resistance to brittle failure, or some combination thereof.In a non-limiting example, a compliant material disclosed herein may besilver. It may be noted that multi-micron-sized and larger silverparticles may be used in bulk superconductors and in thin films, butto-date, the configurations of the 2G HTS tapes herein have not beendescribed. Also, other metals and alloys that are compatible with thesuperconductor may be incorporated into the configurations disclosedherein; such as, but not limited to, ceramics including aluminum oxide,yttria-stabilized zirconia, and titanium-nitride.

In one configuration mentioned hereinabove, a superconducting film iscaptured or sandwiched between compliant films. Generally, the compliantfilms cover at least about 15% of the area of the preceding layer, forexample, the layer below the compliant film. Still further, thecompliant films cover at least about 20% of the area of the layertherebelow; and in certain configurations, the compliant films cover atleast about 25% of the layer beneath it. In some configurations, thecompliant films may include a metal, an alloy, a ceramic, or a compositethereof. In certain configurations, the metal, alloy, or ceramic maycomprise an oxide. Without limitation by any particular theory, thecompliant layer comprises a material with a high ductility, a highfracture toughness, or a combination thereof. In exemplaryconfigurations, the compliant layer comprises a metal such as but notlimited to silver or an alloy thereof, disposed on the substrate. Thesuperconducting layer is deposited thereon, for instance by a metalorganic chemical vapor deposition process (MOCVD). In other exemplaryconfigurations, the superconductor layer is deposited on a substrate anda compliant layer is deposited thereon. In certain configurations, thesubstrate comprises a continuous epitaxial thin film of a compliantfilm, such as silver. Subsequently, a silver overlayer may be depositedsuch that the superconductor is captured, partially encapsulated, or“sandwiched” between the silver layers. The superconductor film iscontained fully between two compliant or ductile film layers asdescribed to provide the disclosed transverse tensile strength.

Further, the compliant film may be deposited on the substrate or entailthe epitaxial growth of the compliant film on the substrate, prior todeposition of the superconducting material. The compliant film such assilver or a similarly compliant/ductile film may be grown on abiaxially-textured template to form the substrate. Further, afterdeposition of the superconducting material, additional layers ofcompliant film may be grown epitaxially thereon. Thus, this step ofepitaxial growth may precede or follow the epitaxial growth ofsuperconducting film. For example, the process of epitaxial growth ofsilver film on biaxially-textured MgO grown by ion beam assisteddeposition on a metal substrate has been successfully demonstrated.Referring now to FIG. 4(a), there is shown the theta-2theta patternobtained by X-Ray Diffraction (XRD) from an exemplary silver filmaccording to one configuration of the present disclosure. A stronglytextured silver orientation along (200) is observed in the Figure and noother orientations of the metal are seen. FIG. 4(b) displays the XRDpolefigure (111) of the epitaxial silver film, illustrating the in-planetexture of about 2° full-width, half-maximum (FWHM) has been achieved.Without limitation by any particular theory, the biaxially-textured filmenables epitaxial growth of superconducting film in a subsequentprocess.

In another configuration, the superconducting film is deposited on acompliant material layer that includes a discontinuous array ofnanomaterials, the layer comprising a compliant or ductile material ormetal, such as but not limited to, silver. In instances, this compliantmaterial layer includes nanomaterial that covers at least about 15% ofthe area of the preceding layer, for example, the layer below thecompliant film. In other instances, the compliant film material includesa discontinuous array of nanomaterial that covers at least about 20% ofthe area of the layer therebelow; and in certain configurations, thecompliant film material includes a discontinuous array of nanomaterialthat covers at least about 25% of the layer beneath it. In certaininstances, a composite of oxide-silver is deposited epitaxially on abiaxially-textured template. Subsequently, the superconductor film isdeposited thereon the compliant material layer having the discontinuousarray of nanomaterial. In certain configurations, this may result inimproved fracture toughness, for example to the oxide buffer layer, andstronger bonding between the superconductor and the overlayer orsubstrate layers.

Referring to FIG. 5, the superconductor film 10 is deposited onto thecompliant layer, for example the nanomaterial array comprising compliantnanomaterials, and in certain instance, comprising compliantnanoparticles. In instances, the nanomaterials or nanoparticles areductile, exhibit high fracture toughness, resistance to brittle failure,or some combination thereof. As previously disclosed herein, suitablecompliant nanoparticles comprise silver, or other nanomaterialsparticles having similar properties, without limitation. In certaininstances, the nanomaterial array 20 comprises a discontinuous array ofnanoparticles. The nanoparticles of the nanomaterial array 20 cover atleast about 20% of the area of the layer therebelow; and in certainconfigurations, the nanoparticles of the nanomaterial array 20 cover atleast about 25% of the layer beneath it. The nanomaterial array 20 maybe formed by deposition of an incomplete or thin film on the oxidebuffer layer 30 followed by deposition of the superconducting layer 10.The thin film does not have to be epitaxial and thus may be deposited onthe oxide buffer at a low temperature. More specifically, thenanoparticles are first formed on the oxide buffer layer 30, supportedon the substrate 40. As disclosed herein, under conditions wherein thefilm is incompletely deposited or significantly thin, for example lessthan about 0.5 μm, the film decomposes or contracts during subsequentheat treatment, into the nanomaterial array 20 comprising adiscontinuous array of nanoparticles. Referring to FIG. 5(a) the smalldots on the comprising the nanomaterial array 20 represent thenanoparticles that are shown in the photomicrograph found in FIG. 5(b).

Misoriented grains in the superconducting film result from the failureto maintain an optimum temperature during thick film growth. Morespecifically, when temperature decreases to below about 30° C. below theoptimum temperature, the epitaxial growth of the superconducting film isaffected, resulting in misoriented or misaligned grains in thesuperconducting film that reduce critical current density and reducemechanical strength of the article. In the configurations describedabove with respect to FIGS. 4 and 5, the distribution of silverparticles within the superconducting film provides liquid-phase assistedgrowth that functions to lower the optimum deposition temperature to amore suitable range to prevent or reduce misoriented grain growth. Thesuperconductor-silver composite could be deposited at a lower optimumtemperature, for example between about 20° C. and about 50° C. below theoptimum temperature required for a depositing superconductor filmwithout silver. Thus, the misoriented grain growth that is deleteriousto electrical and mechanical properties may be avoided.

Thus, as illustrated in FIG. 6, in another configuration, a film ofcompliant material that includes a discontinuous array 20 ofnanoparticles may be deposited within the superconducting film 10. Ininstances, similar to the previous descriptions, silver or discontinuoussilver and other suitably compliant or ductile metals may be depositedwithin the superconducting film 10. For example, without limitation, theprocess may be initiated as described hereinabove to deposit a firstsuperconducting layer 10 a on a template or other support forsuperconductor deposition, such as the buffer layer 30. Subsequently, asignificantly thin layer of compliant material, for example silver filmhaving a thickness of less than about 0.5 μm, is deposited on the firstlayer of superconducting film 10 a. The thin film of compliant materialself-converts or aggregates into a layer of nanoparticles, forming thenanomaterial array 20. In the present example, the nanoparticles aresilver, although any material or alloy described herein is suitable. Anadditional or second layer of superconducting material 10 b may bedeposited on the nanomaterial array 20. Thus, an epitaxial film isrendered unnecessary and the second superconductor film is growndirectly on the first superconducting film 10 a with a nanoparticlecovering in the nanomaterial array 20. In the completed structure, thesilver nanoparticles are embedded between the two superconducting filmlayers 10 a and 10 b, wherein 10 a is a first superconducting film layerand 10 b is a second superconducting film layer. Furthermore, theprocess disclosed herein may be repeated multiple times to obtain aconfiguration comprising alternating superconductor layers 10 andcompliant nanomaterial array 20 comprising nanoparticles, for example toobtain a superconductor with several superconducting layers, includingmore than 5 superconducting layers, as an example. Additionally, thisconfiguration may be combined with that described in FIG. 5 to form asuperconducting tape configuration or architecture as illustrated inFIG. 7. In this latter configuration, the nanoparticles of thenanomaterial array 20 impart improved interfacial bonding between theoxide buffer layer 30 and the superconductor layers 10 as well asimproved delamination strength of the superconductor in the finishedproduct compared to conventional HTS tapes. Additionally, the silverparticles can prevent crack initiation or growth that could propagatewithin the bulk of the superconducting film when the tape is subjectedto a transverse tensile or bending stress.

Extrapolating the disclosure, the illustration in FIG. 8 further showsthat the disclosed process of alternating layers of superconductor 10and compliant nanomaterials 20 may be applied to compliant material thinfilms. More specifically, the thin films of compliant nanomaterial 20,for example silver, grown epitaxially as described hereinabove, may berepeated a plurality of times in order to form a stack or stacked“sandwich” of the compliant layers 40 with a superconducting layers 10between each of the compliant layers 40, to form an plurality ofalternating layers. The process to achieve that configuration comprises,in addition to the first epitaxial film on oxide, additional compliantmaterial films that are deposited in an alternating sequence onsuperconducting films. This configuration may be envisioned as shown inFIG. 8. Further, as there are a plurality of layers of thesuperconducting film, elimination of the misoriented and misalignedgrains is possible within the scope of the present disclosure. Bydepositing each superconducting film layer in a significantly thinlayer, for example, less than about 1 μm, the random growth ofmisoriented grains seen in thick films of certain conventionalsuperconducting tapes is avoided. Still further, the relatively thinsuperconducting film layers captured in or sandwiched between compliantfilm layers results in a configuration or architecture of the HTS tapewith improved mechanical properties.

Exemplary embodiments are disclosed herein and variations, combinations,and/or modifications of such embodiment(s) may be made by a personhaving ordinary skill in the art and are within the scope of thedisclosure. Alternative embodiments that result from combining,integrating, and/or omitting features of the expressly-disclosedembodiment(s) are also within the scope of the disclosure. Unlessexpressly stated otherwise, the steps in a method claim may be performedin any order. The recitation of identifiers such as (a), (b), (c) or(1), (2), (3) before steps in a method claim are not intended to and donot specify a particular order to the steps, but rather are used tosimplify subsequent reference to such steps. Where numerical ranges orlimitations are expressly stated, such express ranges or limitationsshould be understood to include iterative ranges or limitations of likemagnitude falling within the expressly stated ranges or limitations(e.g., from about 1 to about 10 includes, 2, 3, 4, etc.; greater than0.10 includes 0.11, 0.12, 0.13, etc.). For example, whenever a numericalrange with a lower limit, R_(l), and an upper limit, R_(u), isdisclosed, any number falling within the range is specificallydisclosed. In particular, the following numbers within the range arespecifically disclosed: R=R_(l)+k* (R_(u)-R_(l)), wherein k is avariable ranging from 1 percent to 100 percent with a 1 percentincrement, i.e., k is 1 percent, 2 percent, 3 percent, 4 percent, 5percent, . . . 50 percent, 51 percent, 52 percent . . . 95 percent, 96percent, 97 percent, 98 percent, 99 percent, or 100 percent. Moreover,any numerical range defined by two R numbers as defined in the above isalso specifically disclosed. Use of the term “optionally” with respectto any element of a claim means that the element is required, oralternatively, the element is not required, both alternatives beingwithin the scope of the claim. Use of broader terms such as “comprises”,“includes”, and “having” means “including but not limited to” and shouldbe understood to also provide support for narrower terms such as“consisting of”, “consisting essentially of”, and “comprisedsubstantially of.” Accordingly, the scope of protection is not limitedby the description set out above but is defined by the claims thatfollow, that scope including all equivalents of the subject matter ofthe claims. Each and every claim set out below is incorporated into thisspecification as additional disclosure, and each is an exemplaryembodiment of the present invention. All patents, patent applications,and publications cited in this disclosure are hereby incorporated byreference, to the extent that they provide exemplary, procedural orother details supplementary to the disclosure.

I claim:
 1. A superconductor structure comprising: a substrate; acompliant material array; a superconducting layer disposed on top of thecompliant material array; and an overlayer, wherein the compliantmaterial array comprises nanoparticles having a size of less than about0.5 μm.
 2. The superconductor structure of claim 1, wherein thecompliant material array comprises at least one material chosen from thegroup consisting of metals, alloys, ceramics, and combinations thereof.3. The superconductor structure of claim 1, wherein the compliantmaterial array comprises a material having one property chosen from thegroup consisting of high ductility, a high fracture toughness, or acombination thereof.
 4. The superconductor structure of claim 1, whereinthe compliant material comprises silver.
 5. The superconductor structureof claim 1, wherein the compliant material covers at least 15% of thesurface area of the layer beneath it.
 6. A superconducting tapestructure comprising: a substrate; a first superconducting layer; acompliant material array; a second superconducting layer; and anoverlayer, wherein the compliant material array comprises nanoparticleshaving a size of less than about 0.5 μm, the compliant material arraybetween and directly contacting the first superconducting layer and thesecond superconducting layer.
 7. The tape structure of claim 6, whereinthe compliant material covers less than approximately 50% of the surfacearea of the layer beneath it.
 8. A superconductor structure comprising:a substrate; a first superconducting layer; a compliant material layer;a second superconducting layer; and an overlayer, wherein each of thefirst and the second superconducting layer has a thickness of less thanabout 1 μm, and wherein the compliant material layer is epitaxiallygrown between and directly contacting the two superconducting layers. 9.The superconductor structure of claim 8, wherein the compliant materiallayer comprises a biaxial texture.
 10. The superconductor structure ofclaim 8, wherein the compliant material layer comprises at least onematerial chosen from the group consisting of metals, alloys, ceramics,and combinations thereof.
 11. The superconductor structure of claim 10,wherein the compliant material layer comprises a material having oneproperty chosen from the group consisting of high ductility, a highfracture toughness, or a combination thereof.
 12. A superconducting tapestructure comprising: a substrate; a plurality of superconductinglayers; and a plurality of compliant material layers; wherein theplurality of compliant material layers comprises at least one array ofnanoparticles having a size of less than about 0.5 μm, and wherein atleast one of the plurality of compliant material layers is between anddirectly contacting two superconducting layers in the plurality ofsuperconducting layers.
 13. The tape of claim 12, wherein at least oneof the plurality of compliant material layers covers less thanapproximately 50% of the surface area of the layer beneath it.
 14. Asuperconducting tape structure comprising: a substrate; a plurality ofsuperconducting layers; and a plurality of compliant material layers;wherein the plurality of compliant material layers comprises at leastone epitaxially oriented layer that is in direct contact with twosuperconducting layers in the plurality of super conducting layers.